GEOMAGNETIC-ACTIVITY AND THE BETA-DEPENDENCE OF THE DAYSIDE RECONNECTION RATE

In previous work we have used geomagnetic activity as a proxy measure of the reconnection rate to determine how die upstream solar wind para meters control reconnection. Herein we extend that work to show how th e solar wind magnetosonic Mach number, upstream solar wind beta, and t he cone angle of the interplanetary magnetic field are correlated with a proxy measure of the efficiency of the reconnection process. Each o f these three parameters controls the plasma beta in the magnetosheath downstream of die Earth's bow shock. The dependence of die efficiency of reconnection on the above parameters is in agreement with the expe ctation that large magnetosheath betas reduce the rate of or hinder th e onset of dayside reconnection.